Acute pancreatitis is characterized by the pathologic activation of zymogens within pancreatic acinar cells. The process requires a rise in cytosolic Ca 2؉ from undefined intracellular stores. We hypothesized that zymogen activation is mediated by ryanodine receptor (RYR)-regulated Ca 2؉ release, because early zymogen activation takes place in a supranuclear compartment that overlaps in distribution with the RYR. Ca 2؉ signals in the basolateral, but not apical, region of acinar cells observed during supraphysiologic agonist stimulation were dependent on RYR Ca 2؉ release. Inhibition of RYR or depletion of RYR-sensitive Ca 2؉ pools each reduced pathologic zymogen activation in isolated acinar cells, but neither treatment affected amylase secretion. Inhibition of RYR also inhibited zymogen activation in vivo. We propose that Ca 2؉ release from the RYR mediates zymogen activation but not enzyme secretion. The findings imply a role for the RYR in acute pancreatitis.pancreatic acinar cell ͉ dantrolene ͉ calcium signaling

Purpose of the review: Pancreatic cancer is extremely aggressive, forming highly chemo-resistant tumors, and has one of the worst prognoses. The evolution of this cancer is multi-factorial. Repeated acute pancreatic injury and inflammation are important contributing factors in the development of pancreatic cancer. This article attempts to understand the common pathways linking pancreatitis to pancreatic cancer.Recent findings: Intracellular activation of both pancreatic enzymes and the transcription factor NF-κB are important mechanisms that induce acute pancreatitis (AP). Recurrent pancreatic injury due to genetic susceptibility, environmental factors such as smoking, alcohol intake, and conditions such as obesity lead to increases in oxidative stress, impaired autophagy and constitutive activation of inflammatory pathways. These processes can stimulate pancreatic stellate cells, thereby increasing fibrosis and encouraging chronic disease development. Activation of oncogenic Kras mutations through inflammation, coupled with altered levels of tumor suppressor proteins (p53 and p16) can ultimately lead to development of pancreatic cancer.Summary: Although our understanding of pancreatitis and pancreatic cancer has tremendously increased over many years, much remains to be elucidated in terms of common pathways linking these conditions.

Clinical studies indicate that cigarette smoking increases the risk for developing acute pancreatitis. The nicotine metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a major cigarette smoke toxin. We hypothesized that NNK could sensitize to pancreatitis and examined its effects in isolated rat pancreatic acini and in vivo. In acini, 100 nM NNK caused three- and fivefold activation of trypsinogen and chymotrypsinogen, respectively, above control. Furthermore, NNK pretreatment in acini enhanced zymogen activation in a cerulein pancreatitis model. The long-term effects of NNK were examined in vivo after intraperitoneal injection of NNK (100 mg/kg body wt) three times weekly for 2 wk. NNK alone caused zymogen activation (6-fold for trypsinogen and 2-fold for chymotrypsinogen vs. control), vacuolization, pyknotic nuclei, and edema. This NNK pretreatment followed by treatment with cerulein (40 μg/kg) for 1 h to induce early pancreatitis responses enhanced trypsinogen and chymotrypsinogen activation, as well as other parameters of pancreatitis, compared with cerulein alone. Potential targets of NNK include nicotinic acetylcholine receptors and β-adrenergic receptors; mRNA for both receptor types was detected in acinar cell preparations. Studies with pharmacological inhibitors of these receptors indicate that NNK can mediate acinar cell responses through an nonneuronal α(7)-nicotinic acetylcholine receptor (α(7)-nAChR). These studies suggest that prolonged exposure to this tobacco toxin can cause pancreatitis and sensitize to disease. Therapies targeting NNK-mediated pathways may prove useful in treatment of smoking-related pancreatitis.

Background and Aims-Protease activation within the pancreatic acinar cell is a key early event in acute pancreatitis and may require low pH intracellular compartments. Clinical studies suggest that acidosis may affect the risk for developing pancreatitis. We hypothesized that exposure to an acid load might sensitize the acinar cell to secretagogue-induced pancreatitis.

A characteristic of acute pancreatitis is the premature activation and retention of enzymes within the pancreatic acinar cell. Because ligands linked to cAMP production may prevent some forms of pancreatitis, we evaluated the effects of increased intracellular cAMP in the rat pancreatic acinar cell. Specifically, this study examined the effects of the cholinergic agonist carbachol and agents that increase cAMP [secretin and 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP)] on zymogen activation (trypsin and chymotrypsin), enzyme secretion, and cellular injury in isolated pancreatic acini. Although cAMP agonists affected the responses to physiological concentrations of carbachol (1 microM), their most prominent effects were observed with supraphysiological concentrations (1 mM). When secretin was added to 1 mM carbachol, there was a slight increase in zymogen activation, but no change in the secretion of amylase or chymotrypsin. Furthermore, coaddition of secretin increased parameters of cell injury (trypan blue exclusion, lactic dehydrogenase release, and morphological markers) compared with carbachol (1 mM) alone. Although directly increasing cellular cAMP by 8-Br-cAMP caused much greater zymogen activation than carbachol (1 mM) alone or with secretin, 8-Br-cAMP cotreatment reduced all parameters of injury to the level of unstimulated acini. Furthermore, 8-Br-cAMP dramatically enhanced the secretion of amylase and chymotrypsin from the acinar cell. This study demonstrates that increasing acinar cell cAMP can overcome the inhibition of enzyme secretion caused by high concentrations of carbachol and eliminate acinar cell injury.

Acute pancreatitis is a disease associated with inflammation and tissue damage. One protein that protects against acute injury, including ischemic injury to both the kidney and heart, is renalase, which is secreted into the blood by the kidney and other tissues. However, whether renalase reduces acute injury associated with pancreatitis is unknown. Here, we used both and murine models of acute pancreatitis to study renalase's effects on this condition. In isolated pancreatic lobules, pretreatment with recombinant human renalase (rRNLS) blocked zymogen activation caused by cerulein, carbachol, and a bile acid. Renalase also blocked cerulein-induced cell injury and histological changes. In the cerulein model of pancreatitis, genetic deletion of renalase resulted in more severe disease, andadministering rRNLS to cerulein-exposed WT mice after pancreatitis onset was protective. Because pathological increases in acinar cell cytosolic calcium levels are central to the initiation of acute pancreatitis, we also investigated whether rRNLS could function through its binding protein, plasma membrane calcium ATPase 4b (PMCA4b), which excretes calcium from cells. We found that PMCA4b is expressed in both murine and human acinar cells and that a PMCA4b-selective inhibitor worsens pancreatitis-induced injury and blocks the protective effects of rRNLS. These findings suggest that renalase is a protective plasma protein that reduces acinar cell injury through a plasma membrane calcium ATPase. Because exogenous rRNLS reduces the severity of acute pancreatitis, it has potential as a therapeutic agent.

Activation of zymogens within the pancreatic acinar cell is an early feature of acute pancreatitis. Supraphysiological concentrations of cholecystokinin (CCK) cause zymogen activation and pancreatitis. The effects of the CCK analog, caerulein, and alcohol on trypsin and chymotrypsin activation in isolated pancreatic acini were examined. Caerulein increased markers of zymogen activation in a time- and concentration-dependent manner. Notably, trypsin activity reached a peak value within 30 min, then diminished with time, whereas chymotrypsin activity increased with time. Ethanol (35 mM) sensitized the acinar cells to the effects of caerulein (10(-10) to 10(-7) M) on zymogen activation but had no effect alone. The effects of ethanol were concentration dependent. Alcohols with a chain length of >or=2 also sensitized the acinar cell to caerulein; the most potent was butanol. Branched alcohols (2-propanol and 2-butanol) were less potent than aliphatic alcohols (1-propanol and 1-butanol). The structure of an alcohol is related to its ability to sensitize acinar cells to the effects of caerulein on zymogen activation.

Supramaximal concentrations of cholecystokinin or its analogue caerulein have been shown to stimulate the proteolytic activation of zymogens within the pancreatic acinar cell and initiate acute pancreatitis. Previous studies suggest that a low pH compartment might be required for activation. To test this hypothesis, the effects of agents that modulate intracellular pH on caerulein-induced trypsin and chymotrypsin activation were studied. Pretreatment of pancreatic acini with the proto-ionophore monensin (10 M) and the weak base chloroquine (40 M) inhibited activation. Pre-incubation with the vacuolar ATPase (V-ATPase) inhibitors bafilomycin A 1 and concanamycin A also decreased activation in a concentration-dependent manner with 50% inhibition at ϳ50 and 25 nM, respectively. Caerulein stimulation caused a time-and concentration-dependent translocation of soluble V-ATPase V 1 subunits to a membrane fraction, a marker of V-ATPase activation. Carbachol also stimulated translocation at supramaximal concentrations. Elevation of cytosolic Ca 2؉ by thapsigargin was sufficient to induce translocation. Thus, stimulation of VATPase activity appears to be required for agonist-induced zymogen activation in the pancreatic acinar cell.The premature activation of digestive zymogens in the pancreatic acinar cell plays a central role in the initiation of acute pancreatitis, but the mechanisms leading to activation remain unclear. Concentrations of cholecystokinin that are at least 10-fold greater than that generated by the physiologic response to a meal, a treatment known as hyperstimulation, cause zymogen activation and pancreatitis in vivo. Similarly, hyperstimulation of isolated pancreatic acini by cholecystokinin or its analogue caerulein causes zymogen activation in vitro (1, 2). Such activation appears to take place in unidentified membrane-bound organelles. Previous findings suggest that the generation of a low pH compartment in acinar cells is a feature of acute pancreatitis and may be required for zymogen activation. First, in both the caerulein hyperstimulation and the choline-deficient, ethionine-supplemented diet models of acute pancreatitis, acidic vacuoles are generated within acinar cells (3). Second, chloroquine, a weak base that non-selectively increases pH in acidic organelles, reduces the severity of pancreatitis in the caerulein hyperstimulation and choline-deficient, ethionine-supplemented diet models of pancreatitis (4, 5). Third, both proposed mechanisms of zymogen activation, trypsinogen autoactivation and trypsinogen activation by the lysosomal protease cathepsin B, proceed optimally at an acidic pH (6). Finally, chloroquine and monensin, agents that non-selectively increase intracellular pH, block the proteolytic conversion of procarboxypeptidase A 1 to its active form in isolated acini following caerulein hyperstimulation (1). Although these studies support a role for acidification in zymogen activation, they provide no information on the mechanism.Because vacuolar ATPase (V-ATPase) 1 acidifies many in...